Xue Song Wang

Removal of chromium (VI) from aqueous solution using walnut hull.

In this study, removal of chromium (VI) from aqueous solution by walnut hull (a local low-cost adsorbent) was studied. The extent of adsorption was investigated as a function of solution pH, contact time, adsorbent and adsorbate concentration, reaction temperature and supporting electrolyte (sodium chloride). The Cr (VI) removal was pH-dependent, reaching a maximum (97.3%) at pH 1.0. The kinetic experimental data were fitted to the first-order, modified Freundlich, intraparticle diffusion and Elovich models and the corresponding parameters were obtained. A 102.78 kJ/mol Ea (activation energy) for the reaction of chromium (VI) adsorption onto walnut indicated that the rate-limiting step in this case might be a chemically controlled process. Both the Langmuir and Freundlich isotherms were suitable for describing the biosorption of chromium (VI) onto walnut hull. The uptake of chromium (VI) per weight of adsorbent increased with increasing initial chromium (VI) concentration up to 240-480 mg/L, and decreased sharply with increasing adsorbent concentration ranging from 1.0 to 5.0 g/L. An increase in sodium chloride (as supporting electrolyte) concentration was found to induce a negative effect while an increase in temperature was found to give rise to a positive effect on the chromium (VI) adsorption process. Compared to the various other adsorbents reported in the literature, the walnut hull in this study shows very good promise for practical applicability.

The removal of basic dyes from aqueous solutions using agricultural by-products

The adsorption of two basic dyes, namely, Malachite Green and Methylene Blue onto both agricultural by-products (i.e. rice bran and wheat bran) has been investigated in this study. The adsorption of both basic dyes was solution pH-dependent. The kinetic experimental data were analyzed using four kinetic equations including pseudo-first-order equation, pseudo-second-order equation, external diffusion model and intraparticle diffusion model to examine the mechanism of adsorption and potential rate-controlling step. The best-fit equation was identified using normalized standard deviation. The Langmuir and Freundich isotherms were used to fit the equilibrium data and the results showed that the Langmuir isotherm exhibited a little better fit to the Methylene Blue adsorption data by both adsorbents while the Freundlich isotherm seemed to agree better with the Malachite Green adsorption. The Gibbs free energy changes at 20 degrees C were calculated and the obtained values supported the conclusion that two dyes molecules adsorbed by physical processes. The effects of particle size, adsorbent concentration and solution ionic strength on the adsorption of the two basic dyes were also studied.

Removal of Cr (VI) with wheat-residue derived black carbon: Reaction mechanism and adsorption performance

The removal of Cr (VI) from aqueous solutions using black carbon (BC) isolated from the burning residues of wheat straw was investigated as a function of pH, contact time, reaction temperature, supporting electrolyte concentration and analytical initial Cr (VI) concentration in batch studies. The effect of surface properties on the adsorption behavior of Cr (VI) was investigated with scanning electron microscope (SEM) equipped with the energy dispersive X-ray spectroscope (EDS) and Fourier transform-infrared (FTIR) spectroscopy. The removal mechanism of Cr (VI) onto the BC was investigated and the result showed that the adsorption reaction consumed a large amount of protons along the reduction of Cr (VI) to Cr (III). The oxidation of the BC took place concurrently to the chromium reduction and led to the formation of hydroxyl and carboxyl functions. An initial solution pH of 1.0 was most favorable for Cr (VI) removal. The adsorption process followed the pseudo-second order equation and Freundlich isotherm very well. The Cr (VI) adsorption was temperature-dependent and almost independent on the sodium chloride concentrations. The maximum adsorption capacity for Cr (VI) was found at 21.34 mg/g in an acidic medium, which is comparable to other low-cost adsorbents.

Biosorption of Zinc from Aqueous Solutions by Rice Bran: Kinetics and Equilibrium Studies

Abstract Rice bran, an agricultural by‐product, was used for the removal of zinc ions from aqueous solution. The work considered the determination of zinc‐biomass equilibrium data in batch system. These studies were carried out in order to determine some operational parameters of zinc sorption such as the time required for the Zinc‐biosorbent equilibrium, the effects of biomass particle size, pH, and temperature. The results showed that pH has an importance effect on zinc biosorption capacity. The biosorbent size also affects the zinc biosorption capacity. The sorption process follows pseudo‐second‐order kinetics. The intraparticle diffusion may be the rate‐controlling step involved in the adsorption zinc ions onto the rice bran up to 30 min. The equilibrium data could be best fitted by the Langmuir sorption isotherm equation over the entire concentration range (40–160 mg/dm3). Thermodynamic parameters, such as ΔG°, ΔH°, ΔS°, have been calculated. The thermodynamics of zinc ion/rice bran system indicate spontaneous and endothermic nature of the process.

Biosorption of Congo Red from Aqueous Solution using Wheat Bran and Rice Bran: Batch Studies

Abstract The batch adsorption experiments were carried out using low-cost agricultural by-products, wheat bran and rice bran, for the removal of Congo red from aqueous solution at pH 8.0 and temperature of 25°C. Effects of important parameters such as contact time, adsorbent concentration, adsorbent modification and ion strength were investigated. The raw biomass and loaded Congo red biomass were characterized by FT-IR. The pseudo-first order equation and pseudo-second order equation were tested and the results showed that adsorption of Congo red followed the pseudo-second order very well. The Langmuir and Freundlich equations were applied to the data related to the adsorption isotherms and the observed maximum adsorption capacities (q m ) were 22.73 and 14.63 mg g−1 for wheat bran and rice bran, respectively. The effects of adsorbent concentration and ionic strength on the Congo red adsorption were marked. The adsorption performance has been significantly improved using rice bran modified by .

Comparison of Basic Dye Crystal Violet Removal from Aqueous Solution by Low-Cost Biosorbents

Abstract The removal of basic dye crystal violet by low-cost biosorbents was investigated in this study using a batch experimental system. The adsorption of crystal violet onto various adsorbents was solution pH-dependent and the maximum removal occurred at basic pH 10.0. The kinetic experimental data were analyzed using pseudo-first-order and pseudo-second-order equations to examine the adsorption mechanism and the intraparticle diffusion model to identify the potential rate controlling step. These results suggested that the adsorption of crystal violet onto various adsorbents was best represented by the pseudo-second-order equation. The suitability of the Langmuir and Freundich adsorption isotherms to the equilibrium data was also investigated at various temperatures for all four sorbents and the adsorption isotherms exhibited Freundlich behavior. The Freundlich constant Kf was 1.55 for alligator weed, 2.33 for Laminaria japonica, 9.59 for rice bran and 5.38 (mg/g)/(mg/L)1/n for wheat bran, respectively at adsorbent concentration 5 g/L, pH 10.0 and 20°C. The thermodynamic parameters (ΔH, ΔG, and ΔS) were calculated and the results showed that the adsorption process for various adsorbents was spontaneous, endothermic, with an increased randomness, respectively. The particle size and the reaction temperature exhibited an insignificant impact on the adsorption equilibrium of crystal violet. The adsorbents investigated could serve as low-cost adsorbents for removing the crystal violet from aqueous solution.

Removal of Copper(II) Ions from Aqueous Solutions Using Natural Kaolinite

The potential of the low-cost adsorbent kaolinite for removing copper(II) ions from aqueous solutions was thoroughly investigated. The effects of relevant parameters, i.e. pH, adsorbent concentration, ionic strength and solution temperature, on the adsorption capacity were examined. The adsorption data followed the Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherms. The maximum adsorption capacity was found to be 16.79 mg/g at a pH value of 6.0, an initial Cu(II) ion concentration of 40 mg/dm3 and a temperature of 313 K. Various thermodynamic parameters, viz. the standard free energy change (ΔG0), the enthalpy (ΔH0) and the entropy (ΔS0), were evaluated for the process with the results indicating that it was spontaneous and endothermic in nature. The dynamics of the adsorption process were also studied and values of the adsorption rate constant and the rate constant for intraparticle diffusion calculated. The activation energy (ΔEa) was found to be 19.84 kJ/mol in the present study, indicating a chemical adsorption process involving weak interactions between the adsorbent and the adsorbate. The interaction between Cu(II) ions and kaolinite is mainly attributable to ion exchange. The adsorption capacity increased with increasing solution pH, decreasing ionic strength and decreasing adsorbent concentration. Kaolinite can be used to separate Cu(II) ions from aqueous solutions.

Removal of Copper (II) Ions from Aqueous Solutions using Na‐mordenite

Abstract The potential to remove copper (II) ions from aqueous solutions using Na‐mordenite, a common zeolite mineral, was thoroughly investigated. The effects of relevant parameters solution pH, adsorbent dose, ionic strength, and temperature on copper (II) adsorption capacity were examined. The sorption data followed the Langmuir, Freundlich, and Dubinin‐Radushkevich (D‐R) isotherms. The maximum sorption capacity was found to be 10.69 mg/g at pH 6, initial concentration of 40 mg/dm3, and temperature of 40°C. Different thermodynamic parameters viz., changes in standard free energy (ΔG0), enthalpy (ΔH0), and entropy (ΔS0) have also been evaluated and the results show that the sorption process was spontaneous and endothermic in nature. The dynamics of the sorption process were studied and the values of rate constant of adsorption, rate constant of intraparticle diffusion were calculated. The activation energy (Ea) was found to be 11.25 kJ/mol in the present study, indicating a chemical sorption process involving weak interactions between sorbent and sorbate. The interaction between copper (II) ions and Na‐mordenite is mainly attributable to ion exchange. The sorption capacity increased with the increase of solution pH and the decrease of ionic strength and adsorbent dose. The Na‐mordenite can be used to separate copper (II) ions from aqueous solutions.

Mineralogical and chemical composition of magnetic fly ash fraction

Magnetic fractions of coal fly ashes from three power plants were obtained by wet magnetic separation method. Quartz and mullite were the crystalline minerals dominating the nonmagnetic fractions. Magnetic fractions contained magnetite, hematite, and, to a lesser extent, quartz and mullite. Iron speciation by Mössbauer spectroscopy indicated the presence of Fe2+ and Fe3+ in aluminosilicate glass in magnetic fractions apart from magnetite and hematite. Chemical analyses revealed that magnetic fractions had about 2.5 times higher concentrations of Co and one to two times higher concentrations of Ni, Cu, Zn, Mo, and Cd. The dominant magnetic minerals were ferrimagnetic, and multi domain and stable single domain grains contributed mainly to the magnetic enhancement of fly ash samples.

Removal of Basic Dye Crystal Violet from Aqueous Solution by Cu(II)-Loaded Montmorillonite

The effects of contact time, reaction temperature, and ionic strength on crystal violet adsorption onto Cu(II)-loaded montmorillonite were studied. The kinetic experimental data were analyzed using pseudo-first-order, pseudo-second-order, and Elovich equations to examine the adsorption mechanism. The result suggested that the adsorption was best represented by the pseudo-second-order equation. The suitability of the Langmuir, Freundich, and Temkin isotherms to equilibrium data was also investigated at 25°C. The maximum adsorption capacity was 114.3 mg dye/g Cu(II)-loaded montmorillonite at adsorbent concentration 1 g/L. The differential heat of adsorption was evaluated and the result showed that adsorption of crystal violet onto the Cu-loaded sample was chemical in nature. The ionic strength and reaction temperature exhibited an insignificant impact on the crystal violet adsorption. The Cu(II)-loaded montmorillonite could serve as low-cost adsorbents for removing crystal violet from aqueous solution compared to the data reported in the literature.